Torsional stepping motor and exciter apparatus therefor

ABSTRACT

A stepping or indexing motor including plural electrical-tomechanical energy transducer devices and a torsionally resilient coupling member for connecting transducer rotor members and for storing rotor member mechanical energy between rotor member movements; the torsionally resilient coupling member also providing starting torque for the stepping motor, and a means for separately driving the inertia component and the friction component of the stepping motor load; the torsionally resilient coupling member also providing a means for achieving high torqueto-inertia and torque-to-motor volume ratios in the motor. In one embodiment a transducer device takes the form of a rotor, a stator, and a winding carried at each end of the coupling member, with the output torque at a motor shaft being derived both from an adjacent transducer device and from energy stored in the torsionally resilient coupling member during a previous distorting of the coupling member; the alternate sequential energizing and deenergizing action subjecting the coupling member to a twisting action and a relaxing action during each step of operation. Electrical circuitry for controlling the flow of energy into the stepping motor and for removing energy from the motor magnetic circuit is also described along with a method for achieving a novel energy conserving release of rotor and stator magnetic engagement.

1111 3,809,989 [451 May 7,1974

TORSIONAL STEPPING MOTOR AND EXCITER APPARATUS THEREFOR [52] US. Cl 1.318/696, 318/685, 310/49 [51] Int. Cl. H0211 29/02 [58] Field of Search318/696, 685, 138, 254;

101/93; 310/49; 3l7/D1G. 6; 323/45 ER [56] References Cited UNITEDSTATES PATENTS 3,495,149 2/1970 Swain 318/138 3,418,541 12/1968 Adams3l7/DlG. 6 3,019,374 l/l962 Ladd 3,17/D1G. 6 3,466,528 9/1969 Adams321/45 3,327,200 6/1967 Corey 321/45 ER 3,697,839 10/1972 Unnewehr318/138 3,453,514 7/1969 Rakess et al.... 318/138 3,364,407 l/1968 Hill318/138 3,560,818 2/1971 Amato 318/138 3,444,447 5/1969 Newell 318/6963,401,323 9/1968 French 318/696 3,560,817 2/1971 Amato 318/138 3,584,2736/1971 Massar 318/138 3,560,821 2/1971 Beling 318/138 3,486,096 12/1969Van Cleave 318/138' 3.573.593 4/1971 Beery 318/696 3,402,334 9/1968Newton 318/696 Assignee:

Filed:

Inventors: John D. Hays, Troy; l-larlen L.

Baswell; Jerry A. Combs, both of Dayton; Dale G. Brown, West Carrollton,all of Ohio The National Cash Register Company, Dayton, Ohio Oct. 12,1971 Appl. No.: 188,420

Primary ExaminerG. R. Simmons Attorney, Agent, or Firm-John J. Callahan;J. T. av ns lavseer H. .3

[57] ABSTRACT A stepping'or indexing motor including pluralelectrical-to-mechanical energy transducer devices and a torsionallyresilient coupling member for connecting transducer rotor members andfor storing rotor member mechanical energy between rotor membermovements; the torsionally resilient coupling member also providingstarting torque for the stepping motor, and a means for separatelydriving the inertia component and the friction component of the steppingmotor load; the torsionally resilient coupling member also providing ameans for achieving high torque-to-inertia and torque-to-motor volumeratios in the motor. In one embodiment a transducer device takes theform of a rotor, a stator, and a winding carried at each end of thecoupling member, with the output torque at a motor shaft being derivedboth from an adjacent transducer device and from energy stored in thetorsionally resilient coupling member during a previous distorting ofthe coupling member; the alternate sequential energizing anddeenergizing action subjecting the coupling member to a twisting actionand a relaxing action during each step of operation. Electricalcircuitry for controlling the flow of energy into the stepping motor andfor removing energy from the motor magnetic circuit is also describedalong with a method for achieving a novel energy conserving release ofrotor and stator magnetic engagement.

25 Claims, 24 Drawing Figures I36 I49 159 175 I69 FORWARD LA FORWARDRRENT LE2 CURRENT 2 TORSIONAL I63 A SHAFT MEMBER STATOR c SWITCH SWIT'CH2 swlT cn 3 swn'crm FIG.

PATENTEU H91 3.809.989

sum 1uF'9 CD F r (\l INVENTORS l JOHN D. HAYS HARLEN BASWELL DALE G.BROWN a O JERRY A.COMBS LO THEIR ATTORNEYS PATENTEDMAY 7 29M SUEU 2 0f 9FIG.3D

FIG.3E

FIGJF INVENTORS JOHN D. HAYS HARLEN L. BASWELL DALE c-; BROWN 8. JERRYA. COMBS W THEIR ATTORNEYS I'MFHTH|W 71974 13,809,989 saw 3 0r 9 JOHN D.HAYS, HARLEN L. BASWELL, DALE G. BROWN 8 JERRY A. COMBS N SEQUENCE FoRsECoND sTEPP|NC 'I CYCLE FORWARD CURRENT a FORWARD CURRENT IN ERE-ATTRAC RoToR F 2ND HOLD Pos|T|o HOLDING WINDING A STATOR C BY SWITCHlROTOR B E H 2,518 m E H 05:58 7; H @5210 OFF SEQUENCE FOR ONE STEPPINGCYCLE SHAFT MEMBER D TORSIONAL I63 I6! I53 v ii] l swlT cHis 0 OFF H0LDRoTDR F PAIENTEII Y 7 I974 COIL E SWITCH COIL E SWITCH2 COIL A SWITCH 3COILA SWITCH 4 FCRwARD CUR- RENT IN A FORWARD CUR- RENT IN E HOLD 20?BOTH RoToRs POSITION HOLDING SWITCH 2 SWITCH l FIG. 8A

OSITION PPING HOLD STE JOHN D. HAYS HARLEN L. BASWELL DALE G. BROWN aJERRY A. comes THEIR ATTORNEYS HOLD IT RE- ATTRAcT ROTOR F AND R R U u cC D D m m 8 mm WT WT RN RN OE OE FR FR M E H 02 M SWITCH 3 ACTED UPONSHEET 8 BF 9 PATENTEDMAY 7 i974 SWITCH I SWITCH 2 SWITCH4 269 ROTOR 8 ISHELD ROTOR B FORWARDYU) 233 wmoms A A ONE COMPLETE STEPPING CYCLE SWITCH2 ROTOR F IS HELD WHILE ACTED UPON FORWARD CUR- RENT IN A FORWARD cuR-RENT IN E HOLD BOTH RoToRs RoToR 5 IS WHILE RoToR F IS POSITION HOLD LEI225 QORWARD I wmome E I RoToR F PATENTEIIIIIY 1 I974 3, 809989 SHEU 8 0F9 367 I/ 365 CLOCK 5 L TI.s 372 72s 375 376 v I I DRIVERI I DRIVER 2DRIVER 3 389 DRIVER 2 l I (3 DRIVER I CASE) l I I I ONJOFF ONE COMPLETEPOSITION HOLD- STEPPING CYCLE me WITH BOTH INCLUDING MOTION ENDS OFSECOND AT BOTH ENDS RESILIENT STEPHNG OF RESILIENT COUPLING CYCLECOUPLING RETAINED INVENTORS JOHN D. HAYS HARLEN L. BASWELL DALE G. BROWN8 JERRY A. COMBS 7 J j L W I DR|VER4 3871 LI 'ri THEIR ATTOR NEYSPATENTEUMAY 7 I974 SHEEI 8 BF 9 INVENTORS JOHN D. HAYS HARLEN L. BASWELLDALE 6. BROWN JERRY YA- comes wwym BY fivaw &

THEIR ATTORNEY S TORSIONAL STEPPING MOTOR AND EXCITER APPARATUS THEREFORCROSS REFERENCE TO RELATED APPLICATIONS The drawings and the detaileddescription of the in- I vention portions of the present application arecommon to two applications for letters patent, application Ser. No.188,419 filed Oct. 12, 1971 and the present application Ser. No.188,420, filed Oct. 12, 1971, both assigned to The National CashRegister Company.

BACKGROUND OF THE INVENTION DESCRIPTION OF THE PRIOR ART Steppingmechanisms or indexing mechanisms for driving transporting devices oradvancing devices have been previously used where it is desirable toadvance tapes, record material, films or the like in incremental mannerand without the use of complex clutch and brake mechanisms. In recentyears the use of stepping motors in processing data has becomeincreasingly common because of the high speed operation and precisepositioning of the driven member possible with a stepping motor; dataprocessing uses of a stepping motor have been limited however by therelatively small output torque available from such motors in the priorart.

Several patents in the prior art contain structures which partiallyresemble various embodiments of the present invention; one example ofsuch prior art is British Patent Number 989,172 issued on theapplication of Alan Stone and Electric and Musical Industries Ltd.

on Apr. 14, 1965. In the Stone patent there is shown a two rotorstepping motor having the rotors mounted on a common shaft andmagnetically engaged by two separate stators. The Stone patent differsfrom embodiments of the present invention in that the Stone rotors arerotationally displaced by less than one-half of the pole pitch whilerotors in embodiments of the present invention are displaced bysubstantially one-half of the pole pitch. In the Stone patent, the rotorshaft is also rigid and massive while the shaft in embodiments of thepresent invention is torsionally resilient.

Another example of prior art partially resembling embodiments of thepresent invention is found in US. Pat. No. 3,143,674 issued on theapplication of G. V. Bond. The Bond patent also concerns a steppingmotor having two rotors which are engaged by two separate stators. Inthe Bond patent, the stepping motor rotors are connected by differentialgearing and are allowed to rotate only through a limited arc ofrotation, this limited arc rotation being converted into continuousoutput shaft rotation by the use of a rotary ratchet and pawl mechanism.The Bond invention also includes a torsion bar used for restoring therotors to their normal position following a limited arc rotation event.The

Bond invention differs from the present invention by its necessaryincorporation of the rachet and pawl mechansim, by its necessaryincorporation of gears connecting the two rotors, by the use of atorsion shaft only for motor resetting and by the mounting of 'rotors ondifferent but concentric shafts.

Other examples of prior art partially resembling embodiments of thepresent invention are found in a series of United States patents issuedto William S. Touchman and to Leonard R. Harper and including US. Pat.Nos. 3,309,988; 3,389,843; 3,468,343; and 3,505,950 respectively. TheTouchman and Harper inventions all involve a torsionally resilient shaftconnected between multiple-toothed rotor members which are excited inintermittent fashion. The Touchman and Harper inventions differ fromthat of the present application in that they necessarily incorporate asource of continuous rotation mechanical energy (a motor) for drivingthe torsion shaft and also necessarily include apparatus for excitingthe rotors and torsion shaft into mechanical resonance through periodicbraking of the rotors.

Yet other examples of prior art mechanisms which partially resembleembodiments of the present invention are found in the series of patentsissued to A. G. Thomas and including US. Pat. Nos. 2,578,648; 2,774,922;2,782,354; 2,787,719; 2,808,556 and 2,830,246. Although each of thesepatents concerns a stepping motor having multiple rotors which arerotationally displaced from each other on a common shaft, none of thesepatents incorporates the torsionally resilient shaft or the principle ofstoring energy in a torsionally resilient shaft as found in the presentinvention.

Yet another example of prior art apparatus which partially resemblesembodiments of the present invention found in an article published inthe McGraw-I-lill Company magazine Electronics on Aug. 3, 1970 at page74. In this article, inventor Joseph Gaon describes a relay activatingcircuit which partially resembles excitation circuitry employed withstepping motors of the present invention. The Gaon circuit differs fromthat of the present invention by the absence of switching devicesselected for having breakdown mode energy dissipating capability, by thepositive limitation of Gaons circuit to relay apparatus, by thelimitation of components in Gaons circuit to stated relativevalues andby the'absence of apparatus in Gaons circuit for providing reversecurrent capable of canceling residual magnetism in the excited magneticstructure.

While these examples of the prior art disclose particular constructionsfor stepping motors and related apparatus, they do not show the simpleand low cost combination of torsionally resilient members coupling therotors of two or more incremental motion electrical-tomechanicaltransducer devices nor do they show this simple combination excited bymechanical energy conserving exciter apparatus.

SUMMARY OF THE INVENTION The present invention relates to steppingmotors and more particularly to a stepping motor having a torsion shaftwhich mechanically stores energy therein. An exciting winding iscarriedby each stator of the stepping motor, the winding being energized by adriver controller which supplies energy to the motor and initiatescapture, hold and release events for the rotor teeth.

In operation of the stepping motor, the driver controller causes energyto be stored within the torsionally -3 resilient coupling member byholding one rotor member in a fixed position while the other rotormember is "moved against torque from the resilient coupling member intoa stepping position.

The driver-controller isprovided with capability for accomplishing aquick release of a rotor member from a stepping position in order thatenergy stored in the torsionally resilient coupling member be preservedand not dissipated by generator action occurring during a rotor releaseevent. For accomplishing the quick release sequence, thedriver-controller includes capabil- I ity for rapid dissipation ofenergy stored in the motor electromagnetic structure and capability forcanceling the residual magnetism flux in the motorstructure.

In view of the above discussion, it is an object of the presentinvention to provide a .steppin gmotor having very'high torque output;the torque output being in some instances more than an order ofmagnitude increased over that-of a similarly sized prior art steppingmotor.

Another object of the present invention is to provide a steppingmotorwherein mechanical energy is stored in a torsional shaft memberduringpart-of an operating cycle. i

An additional object of the presentinvention is'to provide a steppingmotor wherein a portion of the output motion approximates simpleharmonic motion.

A further object of the present invention is to provide a low coststepping motor.

7 A further object of the present invention is to provide a double rotorstepping motor wherein the maximum torque generated by a first one ofthe rotors directly adds to the maximum torque generated ,by the secondrotor even though, the first and second rotors are rotationallydisplaced from each other on a common shaft and are notsimulta'ne'ouslyengaged by stator members.

' A further object of the present invention is to provide a steppingmotor having large starting torque.

Still a' further object of the present invention is to provide astepping motorwherein the means employed for generating starting torquealso provides useful load driving torque. v

Still another object of the present invention is to provide asteppingmotor' wherein the rotonportion is highly damped while entering andbeing retained ina stepping position thereby providing a stepping motorhaving little oscillation or overshoot at each stepping position.

Still an additional object of the present invention is .to provide incombination with an'electrical circuit a torsional stepping motorwherein mechanical energy may be efficiently transferred betweenportions of the motor .via a torsional element.

' Still a further object of the present invention is to provide incombination with an electrical circuit a torsional stepping motorwherein the release of a rotor member from magnetic engagement with astator member occurs within a small fraction of the time required forone cycle of mechanical oscillation in the rotor and torsional elementcombinatiom Still another object of the present invention is to providean electrical circuit capable of accomplishing rapid decay and reversalof magnetic flux in a ferromagnetic structure.

Still an additional object of the present invention is to provide anelectrical circuit that is capable of both rapidly dissipating energystored within the magnetic field 'of a ferromagnetic apparatus and ofsupplying additional energy for establishing areversemagnetomotive forcewithin the ferromagnetic apparatus, an apparatus wherein the changebetween energy dissipating and energy supplying functions occursquickly. Still a: further object of the present invention. is to providean electrical circuitcapable of performing the energy dissipating andenergy supplying functions for a ferromagnetic apparatus while employinga minumum of .componentjparts therein. I I

Still another object of the present invention is to provide a method foractuating a torsional stepping'motor.

of energy stored in a torsionally resilient shaft and enwithinthe motor.a I

Additional advantages and features of the present in vention willbecomeapparent and fully understood from a reading of the followingdescription taken together with the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings attached to thepresent specification:

ergy transferred during magnetic tooth attraction FIG. 1 is acrosssectionalview of a stepping motor made'according to the-presentinvention;

FIG. 2.is an end view taken from the right hand side of the motor shownin FIG. 1; I

FIG.I3' (including views 3A to 3F) is a diagrammatic view of a steppingmotor made according to the present inventionaand showing severalrotor-stator relation- "shipsocc urring during stepping action thereof;

FIG. 4 is a-perspective view of another stepping motor made according tothe present invention;

FIG. Sis an exploded view of the FIG. 4 stepping motor;

FIG. 6 (including parts 6A and 6B) is a cross sectional and side view ofa third stepping motor made according to the present invention; 7

FIG. 7 (including views 7A and 7B) is a first electri-, cal schematicand waveform diagram describing an excitation circuit for steppingmotors made according to the present invention;

FIG. 8 (including views 8A and 8B) is a second electrical schematic andwaveform diagram describing an excitation circuit for stepping motorsmade according to the present invention;

FIG. 9 (including views 9A, 9B, and 9C) is an electrical schematic andwaveform diagram describing a logical timing circuit for exciting astepping'motor made according to the present invention; i

FIG, 10 (on the sheet with FIGS. 6A and 6B)and i eluding views 10A, 10B,and 10C) is an electrical enematic and waveform diagram showing detailedper tion of the circuitry shown in FIGS. 7 andv present FIG. 11 is across sectional diagrammatic view of a third stepping motor madeaccording tothe present invention;

' FIG. 12 is a diagrammatic view of a fourth stepping motor madeaccording to the present invention; and

FIG. 13 is a diagrammatic view of a fifth stepping motor made accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction One embodiment of astepping motor made according to the present invention provides anoutput torque of 90 inch-pounds (I440 inch-ounces) while occupyingsubstantially the same volume of space as the best available prior artstepping motor providing an output torque of 50 inch-ounces. The largertorque of the present invention stepping motor results from efficientmagnetic engagement of 40 rotor-stator pole pairs in the stepping motor,as compared with only four rotorstator pole pairs in the conventionalmotor, along with the addition of torque from two rotors at the steppingmotor output shaft of the present motor. Since the invention motorgenerates starting torque without the incorporation of rotor poles thatare energized in a sequence of different time phases, thetorque-to-inertia ratio of the present motor compares favorably withthat of prior art stepping motors.

The structural elements needed to achieve the performance of the presenttorsional stepping motor are known in the prior magnetic and torsionalpendulum arts; however, a successful combination of these structuralelements into a practical torsional stepping motor has been absentbecause of the large losses of mechanical energy that have prevailedwhen magnetic flux was manipulated in an attempted stepping motor;mechanical energy loss, occurring when an engaged stepping motor rotoris released by slowly decaying magnetic flux, has been especiallydifficult to overcome, and this loss has obscured the performancebenefits possible from an energy transferring torsionally resilientstepping motor apparatus.

Since the mechanical structure for transferring energy between portionsof a torsional stepping motor, the electrical circuitry for initiatingthis transfer, and the method of cooperatively operating the mechanicalstructure and electrical circuitry are all important aspects of thepresent invention, the detailed description of the invention in thisspecification includes sections devoted to mechanical description of theinvention, electrical description of the invention, and energy transferdescription of the invention; the attached claims also concern each ofthese three areas of the invention.

In describing the present invention, the name stepping motor couldproperly be applied to either that apparatus located at one end of thetorsionally resilient coupling member, (including a rotor, a stator,electrical windings, bearings, etc.) or to the complete assemblyincluding two or more rotors, two or more stators, two or more sets ofelectrical windings and a torsionally resilient element. In thefollowing specification, the phrase stepping motor is primarily used todescribe that apparatus which includes a torsionally resilient elementand two or more rotor-stator assemblies; in the claims portion of theapplication adherence to this convention is somewhat relaxed with theclaim language being self explanatory. Where the name stepping motor isreserved for the combination of two or more magnetic devices with atorsionally resilient element, the name magnetic exciter or energytransducer or incremental motion rotary magnetic exciter or the namesrotor member and stator member are employed to indicate the apparatuslocated at the ends of the torsionally resilient element.

MECHANICAL DESCRIPTION In FIGS. 1 and 2 of the drawings, there are showntwo views, a sectional view and an end view of a stepping motorconstructed according to the present invention; in FIGS. 1 and 2 themotor is carried on mounting plates 12 and 14 secured to a cylindricalmotor housing 16, which housing separates rotor-stator assemblies 18 and20 and provides support therefor. Rotor-stator assembly 18 comprises apair of stator halves 22 and 24 circumferentially enclosing a rotor 26secured to one end of a torsion shaft 30. Assembly 20 comprises a pairof stator halves 32 and 34 enclosing a rotor 36 that is secured to the.other end of the shaft 30. The shaft 30 is journaled in bearings such asball bearings 45 and 46 supported from bearing housings 47 and 48,respectively, the housings forming the ends of the motor. Stator halves24 and 32 are secured to the motor housing 16 by any convenient meanssuch as the screws 49; stator halves 22 and 34 are, in turn, secured tostator halves 24 and 32, respectively, by some convenient means such ascap screws 50 aided in alignment of the parts with dowel pins 51. Thebearings 45 and 46 may be suitably retained in the housings 47 and 48 bymeans of clips 52 and 53.

The rotor-stator assemblies 18 and 20 in the FIGS. 1 and 2 motors aremagnetic exciter units, having a single time phase electrical circuitand a single time phase magnetic circuit. The FIGS. 1 and 2 motorsinclude a coil contained by stator halves 22 and 24, anda coil 61contained by stator halves 32 and 34, the stator halves 22 and 24 beingseparated at their pole face ends by an air gap 62 with stator halves 32and 34 having a like air gap 63. In the FIGS. 1 and 2 motors, each rotoris provided with 24 equally spaced rotor teeth on the outerperipherythereof to match with 24 companion stator teeth on the inner peripheryof the associated stator. The 24 teethrotor-stator construction (aslabeled by the 24 alphabet letter designations a, b, c, through v, w, xin FIG. 2) provides an angular spacing of 15 degrees between teeth;other constructions of motors according to the present invention may,for example, include 64 teeth with a spacing of five and a fractiondegrees or may include any whole number of teeth.

The magnetic flux path for the rotor and stator halves at the end of themotor where output shaft 28 is located consists of a circular path thatincludes stator half 24, the air gap between stator half 24 and rotor26, the rotor 26 itself, the air gap between rotor 26 and stator half 22and stator 22 itself. A given stator half, such as stator half 24,assumes a single magnetic polarity, for example North, throughout itsperiphery during motor actuation, there being no division of statorteeth into form of lead wires 70 and 71 and connected to a tenninalblock 72 in the FIGS. 1 and 2 motor. An exciter apparatus such as thatdescribed in FIGS. 78, 8B, 9A, 9B, 9C and 10A of the drawings is shownand identified with the number 75 in FIG. 2, this exciter apparatusbeing connected by lead wires 73 and 74 to the motor of FIG. 2.

FIGS. 3A to 3F.of the drawings show a sequence of operation involvingthe capturing, holding, and releasing of motor rotors by the statorsduring stepping operation of a motor which is constructed according tothe present invention. FIG. 3A shows an initial or quiescent conditionof the motor in a position wherein the teeth of rotor 26 at shaft end 28are aligned with the teeth of stator halves 22 and 24; in the FIG. 3views of the motor the numbers 22 and 24 designate both halves of thecomplete stator located at the shaft end 28 of the motor, these halvesbeing represented by the single stator indicated at 22, 24. At the timewhen the teeth of rotor 26 at shaft end 28 are aligned with the teethofstator 22, 24, the teeth of rotor 36 at shaft end 38 are misaligned bysubstantially one-half of a step position or ISO electrical degrees sothat the teeth of stator 32, 34 as seen by tooth a of rotor 36 islocated between tooth a and tooth x of stator 32, 34; the misalignedcondition being manually established during assembly of the motor withthe aid of equipment such as an assembly jig and locating pin means.

When power is applied to the coil 60 of the motor in FIG. 3A, the teethof rotor 26 are held in the illustrated position, alignedwith theteethof stator 22, 24 in a capturing manner and the torsion shaft 30 isin a relaxed state. After coil 60 is first energized, power is laterap-- plied to coil 61 and the teeth of rotor 36 are attracted to andbecome aligned with the teeth of stator 32, 34, in a capturing manner asseen in FIG. 33; tooth a being aligned with tooth a, tooth x with x,etc. In the FIG. 3B illustration of the motor wherein both coils 60-and61 of the motor are energized, the torsion shaft 30 is in a wound-up ortwisted condition. In this position, the motor is ready for its firststepping motion.

Stepping motion may be commenced in theFIG. 3B motor by de-energizingeither coil 60 or coil 6l to release the distorted torsion shaft 30 fromits wound-up statusQIf coil 60 is released, the rotor 26 starts rotatingclockwise with its teeth moving away from the matching teeth of thestators 22, 24 as the shaft 30 unwinds, as shown in FIG. 3C. At somepoint after the centerline of a rotor 26 tooth moves near or past thecenterline between teeth of stator 22, 24 (FIG. 3C), the coil 60 mayagain be energized so that magnetic force between rotor and statorattracts the teeth of rotor 26 to the next set of stator 22, 24 teeth.Following the attraction as seen in FIG. 3D, rotor 26 tooth a becomeslocked in alignment with stator tooth b, rotor tooth x with'stator tootha, and rotor tooth w with stator tooth x. During this movement into thenew position commencing with de-energization of coil 60, the wound-upcondition of the torsion shaft 30 is relaxed as the shaft end28accelerates in a clockwise direction; when the shaft end 28 has rotatedto the point where a tooth of rotor 26 moves past the centerline betweenteeth of the stators 22, 24, the shaft end 28 begins decelerating byreason of the shaft again goind into a twisted or wound-up condition.Depending upon the type of loading impressed upon the motor and thespeed of motor operation, coil 60 may be re-energized at a point nearthe time when the centerline of a rotor 26 tooth is aligned with thecenterline between teeth of stators 22, 24'or at a point when thecenterline of a rotor 26 tooth has become almost perfectly aligned withthe centerline of a stator 22, 24 tooth.

Following rotation of the rotor 26 into the new aligned position, theopposite coil, coil 61 is deenergized and the distorted torsion shaft30is again released bringing about a condition where the teeth on rotor 36move in a clockwise direction relative to the stator 32, 34 as thetorsion shaft 30 unwinds. Again, at some point near or after thecenterline of teeth on rotor 36 move past the centerline between teethon stator 32,

34, as shown in FIG. 3E, coil 61 is re-energized and magnetic attractioncauses the teeth of rotor 36 to lock on thenext adjacent stator teeth,as seen in FIG. 3F. With tooth a of rotor 36 being aligned with tooth bof stator 32, 34 and the successive teeth aligned as shown, the torsionshaft-30 is wound up again and the output end 28 of the shaft30 is readyfor the next stepping action. The alternate application of power to thecoils 60 and 61, to obtain acceleration and deceleration of the shaftends and rotors into the next tooth position with the resulting torquebeing built-up and then released within the shaft, accomplishes astepping action at the shaft output end. If a point near the center oftorsion shaft 30 is considered as a reference, the motion of the motormay be compared to the act of a person walking, since the motor motionconsists of a first rotor being held immobilized while the second rotoris advanced from a lagging to a leading position followed by the secondrotor being held immobilized while the first rotor is advanced from alagging to a leading position. The sequence of capturing, holding, andreleasing the rotor by means of energizing and de-energizing' therespective electrical coils provides for energy storage in the torsionshaft 30 as is explained later is this specification. The acceleration,deceleration, and locking action of a motor built accordingto theinvention are sure and positive by reason of every rotor tooth beingaligned with a respective stator. tooth while the motor is in anenergized condition. The motor is capable of producing large outputtorque per unit of rotor inertia since every rotor tooth is acted uponby magnetic flux and no rotor teeth are inactive or reserved for use ina later time phase or'in starting the motor. The torque-to-inertia ratiois large for the motor because the rotor magnetic flux is largelyconfined to the rotor teeth area and need not enter the central regionof the rotor which may therefore be made very small and light in weight.

ENERGY RELATIONSHIPS DESCRIPTION Previous attempts to combine twoincremental motion rotary magnetic exciters and a torsional element havenot been successful primarily because the energy losses in theincremental motion rotary magnetic exciters, located at the torsionalelement ends, were relatively large with respect to the quantity ofenergy which could be stored by the torsional member; the large energylosses thereby serving to effectively mask the energy storage benefitswhich are possible in such a combination. In working with theembodiments of the present invention, it has been found that thepossible sources of energy loss in the motor are so large as to make theamount of energy storable in the torsional member insignificant andimpotent with respect to motor operation if special energy conservationprovisions are not made. A major portion of the notable success of thepresent invention motor can be attributed both to an early realizationof the magnitude these en ergy loss mechanisms can assume, and to anapproach that was found for curtailing energy losses in two areas of themotor. In the present part of this specification, the energy lossmechanisms are described along with preferred embodiment descriptions ofthe apparatus overcoming these energy losses; this section of thespecification also includes an operating description of the motor interms of the energy flow into, within, and out of the motor.

In describing FIG. 3C of the drawings in the preceding mechanicalportion of the specification, it was mentioned that electricalexcitation for coil 60 is removed at one point in the motor operatingcycle in order to permit the wound-up torsion shaft member 30 to relaxand thereby accelerate rotor 26 in the clock-wise direction indicated byarrow 27. From an energy viewpoint, this acceleration of rotor 26involves transferring a quantity of potential energy from therotationally distorted torsion shaft member 30 into the rotor 26 wherethe energy is converted into kinetic energy that is vested in motion ofthe rotating mass of rotor 26. In essence, the potential energy storedin torsional shaft member 30 is converted into kinetic energy whichmoves rotor 26 over a period of time during the interval followingrelease of rotor 26 by coil 60. The efficiency with which energy storedin torsional shaft member 30 can be converted into kinetic energy inrotor 26 is important in motors made according to the present inventionfor several reasons:

I. With efficent energy transfer, the energy available at output shaft28 end of the motor is not limited to that quantity which may betransmitted into the motor via coil 60 but may also include energytransmitted into the motor via coil 61; the use of two input coilshaving advantages insofar as motor inertia, heat dissipation, magneticsaturation and coil electrical time constants are concerned.

2. When energy can be efficiently stored and transmitted between rotorsof the motor, as shown in FIG. 3, itis unnecessary to provide for thegeneration of starting torque in either of the rotary magnetic excitersof the stepping motor; the freedom from rotor poles that are needed onlyfor starting torque generation allows the motor to have lower rotationalinertia and also provides for higher output torque in a given physicalmotor size since all of the included motor poles are utilized for torquegeneration and no poles are reserved for use in sequential time phasesof motor operation. The combination of rotor 26 and rotor 36 also addsuseful load driving torque to the output available from the motor shaft28. In other words, with efficient energy transmission via torsion shaftmember 30, rotor 36 adds both starting torque capability and workdriving torque to the characteristics of rotor 26.

3. If energy can be efficiently transmitted via torsion shaft member 30,the output torque at shaft end 28 of the FIG. 3 motor is mathematicallypredictable with precise accuracy for at least one portion of theoperating cycle of the motor. During the operating cycle portion whenrotation of shaft end 28 is induced by theunwinding of torsional shaftmember 30, the output torque available from shaft end 28 is entirelycontrolled by resilientcharacteristics of the torsion shaft member 30and the motors internal inertia; since these characteristics may beprecisely measured or calculated from the properties of the shaft androtor, the motor output torque is predictable with precision for atleast this torsion shaft driven portion of the operating cycle.

4. If energy can be efficiently transmitted between rotor 36 and rotor26 via torsion shaft member 30, then a combination of friction andinertia load applied at shaft end 28 may be considered as having itsinertia portion driven by torque from'the torsional shaft member 30, andits frictional component driven by rotor 26; although this division ofload driving torques is something less than'mathematically rigorous, itis important in some practical situations since it may be possible toregard torque from the torsion shaft member 30 as having accelerated theload at shaft end 28 up tosome rotational velocity before magnetictorque from rotor 26 is applied. The sequential appearance, at shaft end28, of a known predictable spring torquefollowed by a magneticallyderived motor torque may allow desirable mathematical calculation ofload performance in some motor spplications.

5. If energy can be efficiently transmitted between rotor 36 and rotor26 via torsion shaft member 30, then reversal of the motor rotationdirection involves only selecting between first releasing rotor 36 andfirst releasing rotor 26 when the torsion shaft 30 is in the distortedcondition shown in FIG. 3B of the drawings. In a business machineapplication of the motor, for instance, direction reversal of the motorinvolves nothing more than 'logic signal manipulation to select which ofcoils 60 and 61 is first de-energized following the storage of potentialenergy in torsion shaft member 30.

The efficient transmission of energy from rotor 36 to rotor 26 viatorsion shaft member 30 is found to involve two classes of energy lossmechanisms. The first of these loss mechanisms is attributed tomolecular friction or torsional hysteresis within the torsion shaftmember 30 itself. This torsional hysteresis is similar in nature to themajor energy loss mechanism which prevents a steel ball bearing, whendropped from a height of six feet to a concrete floor, from bouncinghigher than five and a fraction feet upon the first bounce. If therewere no mechanical hysteresis (or windage or other energy lossmechanisms) acting on the ball, all of the kinetic energy vested intheball bearing just prior to impact with the concrete floor would bereturned to the ball and it would be driven to the original point ofdeparture during rebound. In the torsional shaft member 30 of FIG. 3, ifthere-were no molecular friction and mechanical hysteresis losses in thetorsion shaft member 30, (and no wind losses present) then the energyimparted into torsion shaft member 30 by a mechanical twisting of rotor36 through an arc of nine degrees would rotate rotor 26 through anidentical arc of nine degrees upon rotor 26 being released from a holdposition. The presence of molecular friction and mechanical hysteresisin even the best of the practically available materials for torsionshaft member 30, precludes a nine degree rotation of rotor 36 frominducing a nine degree rotation in rotor 26.

In the present invention, it has been found desirable to use a specialclass of materials in the fabrication of torsion shaft member 30 tominimize the losses from molecular friction and mechanical hysteresis inthe motor; among the materials which have been found successful for thisfabrication is the family of steels which are known as electrode typesteels and especially the So long'as the energy losses from molecularfriction steel which is known as American Iron and Steel Institute No.52100 (AlSl 52100) ball bearing steel. When AlSI 52100 ball bearingsteel is employed, it has been found that a torsion shaft member30having a length to diameter ratio near-l6 tol is satisfactory fromboth an energy loss and from a fatigue resistance view-point whenemployed in a stepping motor having nine degree step increments.

Other materials have been successfully employed for fabricating asatisfactory torsion shaft member 30 in some applications; among thesematerials are the alloys of titanium and the alloys of aluminum, such asthose employed in mechanical tuning forks. Aluminum alloys have somedisadvantages for the torsion application, in that they have arelatively low torsional fatigue-stress; on the other hand, titaniumalloys may permit a lower length to diameter ratio for the torsion shaftmember and mechanical hysteresis are maintained within desirable limits,other materials and other shapes for the torv sion shaft member 30 maybe practical in some uses of the motor; for instance, the torsion shaftmember 30 after rotation of rotor 26 commences, does not decayinstantaneously, but rather over an appreciable period of time, a. timethat is measured in milliseconds and is a function of the electricalinductance of coil60, the initial rotation or rotor 26 is not free butis restrained by the remaining magnetic flux between rotor 26 and stator22,'24. Even though the magnetic flux established by coil 60 continuesto decrease as rotor 26 continues to move, the time which elapses beforethe moving rotor 26.is completely free of magnetic flux retardation maybe quitelong, even longer than the time requiredfor. torsion shaftmember 30 to rotate rotor 26 through a full tooth position. In manycases, therefore, it can be stated that the entire motion of rotor 26,be-

tween successive tooth-aligned positions, is. rotation whichis-retardedby the decaying magnetic flux from coil 60, whereprecautionsa're not observed to quickly remove the magnetic fluxestablished by coil 60 from potential-energy for any time period andwill in fact storeits retained potential energy until the restrainingthe release of rotor 26 from magnetic engagement with machinery art. Inthe present invention, it is believed that mostof the energy dissipatedby magnetic hysteresis and electrical eddy currentat de-energization ofcoil 60 comes from the electrical inductance of coil 60 and that only asmall fractionof such loss is'supplied by energy stored within thetorsion shaft member 30. The third energy loss event which is activeupon deexcitation of coil 60 in FIG. 3B arises from generator actionoccurring when the distorted torsionally resilient shaft 30 unwindsfollowing release of rotor 26 by a slowly decreasing magnetic field, themagnetic field decrease in an inductive circuit being inherentlyrelatively slow with respect to the mechanical time constant of thetorsionally resilient shaft and its inertia load. The third energy lossevent may be explained by examining the components in FIG. 38. Prior tothe release of rotor 26 by coil 60, the torsion shaft member 30 is woundup or distorted and rotor tooth w on rotor 26 is aligned with statortooth w of stator 22, 24; in this condition-the torque from torsionshaft "member 30 is opposed by torque from the magnetic flux couplingbetween aligned rotor and stator teeth. At some time after energizationis removed from coil 60, the magnetic flux holding rotor 26 stationaryagainst the torsional force from torsion shaft member. 30 will havedecreased to a sufficient degree that'the torque from'torsion shaftmember 30 is greater than the magnetic torque exerted on rotor 26, andwhile in this condition rotor 26 will begin to rotate. Since themagnetic fluia'remaining force from themagnetic flux has decreasedsufficiently to allow the rotor to proceed with .its rotation; in otherwords it could be asserted that rotation of rotor 26 does not in factoccur until the magnetic flux has decayed to.

a sufficient degree. In lieu of the decaying flux from coil merelydelaying rotation of rotor 26, however,

potential energy within the torsional shaft member 30 being lost and-notconverted into kinetic energy vested in rotor 26, that is, if rotor 26,during the unwinding of torsion shaft member 30, moves between twopoints A and B without realizing an increase in rotor velocity,

then potential energy is'being lost from the motor.

To preserve the potential energy that is stored within torsion shaftmember 30 for desirable uses within the motor and its mechanical load,and to prevent loss of this potential energy, by way of magnetic fluxcoupling with the moving rotor, it is necessary that the magnetic fluxfrom coil 60 be removed as quickly as possible once the coil 60i'sseparated from its source of driving energy; that is, aninstantaneous decay of the flux established by coil 60 ;is desirable.

Rapid removal of the magnetic flux established by coil 60 involvestreating two components of flux; one of these components relates to theenergy stored in the air gap of the motor between rotor 26 and stators22, 24; that is, coil 60 being an electrical inductance has magneticallystored within its air gap a quantity of energy which may be expressedaccording to the mathematical formula E= Ll, where E represents Energy,L represents inductance and l represents current flowing'in inductanceL. According to magnetic theory, this energyis stored in the air gap ofthe inductance or in the flux threading between rotor and stator polesof the 'motor. Removal of the flux associated with the magneticinductance of coil 60 therefore involves removing from the magneticcircuit a quantity of energy by way of an electrical dissipating elementconnected to the terminals of coil 60.

In addition tothe magnetic flux resulting from energy stored in theinductance of coil 60, there is also a component of flux linking rotor26 with stator 22, 24, which is based upon residual magnetism within theferromagnetic structure of rotor 26 and stator 22, 24. This residualmagnetism component of flux can be described by referring to FIG. 10C ofthe drawings.

In FIG. 10C there is shown a set of coordinate axes 457 and 459,representing respectively flux density B and magneto-motive force H; onthese coordinate axes there is impressed a magnetic hysteresis curve ofthe type that is descriptive of a ferro-magnetic structure such as rotor26 and stator 22, 24. In the curve of'FIG. 10C, the point labelled 461might represent the operating condition of the ferro-magnetic structureof the motor shown in FIG. 3C during energized excitation of coil 60;upon removal of energization from coil 60 in FIG. 3C, the flux in themagnetic structure would relax back to the point 463 in FIG. 10C. At thepoint 463, there is zero magneto-motive force (H=) applied to the motorstructure. Even though there is zero magneto-motive force applied to theferromagnetic structure at point 463 in FIG. C, there is yet remaining aconsiderable quantity of magnetic flux in the magnetic structure of themotor, as is represented by the vertical distance between the coordinateaxis origin and the point 463, the distance identified as 462 in FIG.10C. Removal of the magnetic flux represented by the point 463 of FIG.10C, requires that some reverse magnetomotive force be applied to coil60. The necessary reverse magneto-motive force is identified by distance465 along the H axis of FIG. 10C. Upon application of the reversemagneto-motive force represented by the distance 465, the flux withinthe magnetic structure of the motor will fall to the point labelled 467in FIG. 10C. Point 467 represents a flux density near zero, zero fluxdensity being that value which will provide negligible restraining forceagainst the motion of rotor 26 by torsion shaft member 30.

A complete removal of the magnetic flux which links rotor and statormembers of the stepping motor in FIG. 3 requires that both the residualmagnetism component of the flux and the' electrical inductance energyrelated component of the flux be considered and that the sum total ofthese components be reduced to zero magnitude as quickly as possiblefollowing removal of energization from the coil 60 or 61. On electricalcircuit capable of performing both the inductance energy removal fromcoil 60 or 61 and the reverse magnetomotive force excitation of coil 60or 61 and performing these events in rapid automatic sequence isdescribed in the electrical description section of this specificatron.

When the motor of FIG. 3 is operated in a manner that permits efficientenergy transfer from one rotor to the other rotor by way of energystorage in the torsion shaft, operation of the motor may be described interms of energy flows as follows:

FIG. 3, including views 3A through 3F, is used again in describingstepping motor energy flow. In FIG. 3A, a motor is shown with rotor 26magnetically engaged with stator 22, 24 and with coil 60 energized tomaintain the rotor-stator engagement. Rotor 36, in FIG. 3A,

is shown with the rotor teeth being mi s-aligned with the stator teethby one-half of a stepping position or by 180 electrical degrees; in thiscondition, coil 61 is deenergized and torsion shaft 30 is relaxed. Ifelectrical energy is applied to coil 61 so that magnetic flux isestablished therein, rotor 36 is caused to rotateinto the position shownin FIG. 38, wherein its teeth are also aligned with the teeth of itsadjacent stator 32, 34. During this alignment process, a portion of theelectrical energy supplied to coil 61 is transduced by the incrementalmotion rotary exciter which includes stator 32, 34, and rotor 36 intomechanical energy and this mechanical energy is stored in the form ofpotential en-,

ergy within the torsion shaft member 30. In other words, a portion ofthe electrical energy supplied to coil 61 is transduced into rotationalmechanical energy vested in rotor 36 and from thence into potentialmechanical'energy vested in the opposing resilient force of torsionshaft member 30. As the motor is shown in FIG. 3B, the potential energystored within torsion shaft member 30 is ready for release at one of themotor rotors; this release occurs in the events depicted in FIG. 3C ofthe drawing wherein the rotor 26 has been released by removingexcitation from coil 60 and the potential energy stored within torsionshaft member 30 is accelerating rotor 26 in the clockwise direction,

indicated by arrow 27. The acceleration of rotor 26 from an energyviewpoint amounts to potential energy within torsional shaft member 30being transferred into rotor 26 in the form of kinetic energy.

When rotor 26 reaches the point of rotation indicated in FIG. 3C,wherein a center line of the rotor poles is aligned with the center linebetween stator poles, all of the potential energy stored within torsionshaft member 30 has been removed therefrom and is now vested in rotor 26in the form of kinetic energy. The kinetic energy of rotor 26 tends tocarry rotor 26 into a succeeding pole aligned condition as shown in FIG.3D of the drawings. Since the energy transfer from torsion shaft member30 into rotor 26 is less than percent efficient, and since there areenergy losses in the motor and its load, the kinetic energy vested inrotor 26 is not capable of carrying rotor 26 into the fully alignedsucceeding stepposition shown in FIG. 3D but is only capable of carryingit near to this perfectly aligned position. At some point after therotor has reached the position shown in FIG. 3C of the drawing, or evenslightly before the rotor reaches the position of FIG. 3C, coil 60 isagain energized and an additional quantity of energy is therebytransduced into rotor 26 to carry it into the perfectly aligned positionshown in FIG. 3D. Both the kinetic energy which carried rotor 26 awayfrom the misaligned position of FIG. 3C toward the aligned position ofFIG. 3D, and a portion of the energy added to the rotor 26 via coil 60as the rotor 26 neared the perfectly aligned position, are stored intorsion shaft member 30 while the motor is in the condition shown inFIG. 3D; that is, the torsion shaft member 30 in FIG. 3D contains both aquantity of energy derived from rotor 36 and an additional quantity ofenergy added via coil 60 and rotor 26. In this condition, as shown inFIG. 3D, the torsion shaft member 30 is again prepared for the releaseof a rotor being vested with the potential energy which will inducerotation of a released rotor.

Since the quantity of energy stored in torsion shaft member 30 in FIG.3D is substantially the same quantity of energy as was stored in torsionshaft member 30 in FIG. 3B, it is clear that the energy which wassupplied via coil 60 in moving rotor 26 into alignment as shown in FIG.3B is essentially that quantity of energy needed to overcome energylosses in the motorand its load, that is, the kinetic energy of rotor 26is supplemental to the extent needed to rotate rotor 26 against torquefrom the torsion shaft member 30 into the aligned condition of FIG. 3Dby energy supplied from coil 60. Rotation of rotor 26 from the positionshown in FIG. 3B to theposition shown in FIG. 3D may be compared withthe action of a torsional pendulum wherein the potential energy storedin a torsion shaft is converted into kinetic energy of a rotating mass.The motor of FIG. 3 supplements the torsional pendulum concept byaddinga quantity of energy'with each torsional oscillation that issufficientto maintain a constant aptitude of torsional oscillationin themotor rotors. v

In FIG. 3E of the drawings, the potential energy which was stored intorsion shaft member 30 in the FIG. 3D drawing has been released byde-energizing coil 61 and is being transferred into rotor 36; as rotor36 approaches the condition shown in FIG. 3F, coil 61 I may again beenergized to supply an addtional quantity of energy to the torsion shaft30 and carry rotor 36 into the fully aligned position of FIG. 3F.

The best moment for re-energizing coils 60 and 61 during the rotormovement conditions of FIGS. 3C and 3B is dependent upon several factorsincluding the type of load impressed on the motor, the motor operatingspeed, the type of electrical driving circuit used to excite coil 60,andthe mechanical and electrical time constants of the motor. It isclear that once the moving rotor 26 approaches the position shown inFIG. BC (the position of 180 electrical degrees mis-alignment of rotorand stator), with the rotor moving and vested with kinetic energy, thatflux from coil 60 may be applied without danger of drawing rotor 26 backinto the preceding alignment condition of FIG. 33, since the inertia ofrotor 26 will carry it into the succeeding step position shown 'in FIG.3D. It is also true, however, that I premature application of flux fromcoil 60, before rotor 26 reaches the 180 electrical degreesmis-alignment position, will retard the motion of rotor 26 and will beinefficient from an energy viewpoint; such premature flux applicationcan also result in rough and noisy operation of the motor.

Depending on the amount of frictional and inertia loading impressed onthe motor, the time delay between coil excitation and flux establishmentand several other factors, coil 60 in one extreme will be reenergizedvery late'in the rotation of rotor 26 so that flux from coil 60essentially does little more than lock rotor 26 in its attained positionof alignment as shown in FIG. 3D, whereas in the other extremecondition, coil 60 will be re-energized as the rotor nears the 180electrical degrees mis-alignment position so that energy is supplied torotor 26 over a longer period of time. In any event, it is desirablethat coil 60 be're-energized at such a rate and with such peak value ofenergization that there not be a grossly excessive amount of kineticenergy vested in rotor 26 at the time it reaches the condition ofperfect alignment shown in FIG. 3D. If rotor 26 has a grossly excessiveamount of kinetic energy over and above that quantity needed to rotateinto the aligned condition of FIG. 3D, the excess energy will bedissipated in the form of mechanical oscillations of rotor 26 about thealigned position of FIG. 3D and will be dissipated in the form of heatin the ferromagnetic parts and the electrical exciting circuitry of themotor since oscillations about an aligned condition, as in FIG. 3D,induce large flux changes and large voltage changes in winding 60. Theenergy flow path coupling rotor 26 and external electrical dissipationelements is described in the electrical portion of this specification.

In summarizing the energy description of a stepping motor made accordingto the'following' invention, it may be said that the motor applies anelaborate sequence of excitation steps to control energy flow into andout of coils and 61 in order that the relatively small quantity ofmechanical potential energy stored in torsion shaft member 30 may bepreserved and usefully employed. Since the steps performed to quicklyrelease rotors 26 and 36 from the magnetic flux of coils 60 and 61 arein themselves wasteful and dissipative of energy, as is explained in thenext topic of this specification, the overall energy efficiency of amotor made according to the present invention is not high; that is, themotor of this invention, in an attempt to preserve the needed and usefulsmall quantity of torsional shaftmember energy is wasteful oflarger'quantities of electrical energy. In many motor applications, ithas been found that overall efficiency is a secondary consideration ascompared with the desirable operating performance.

Throughout the specification and claims of the present application forletters patent, several names are employed in referring-to components ofthe steppingmotor; the torsion shaft member is for instance variouslycalled the torsion shaft, the torsion shaft member, and the torsionallyresilient coupling member; in similar fashion, the energy transducerdevices located at each end of the torsion shaft member are variouslycalled incremental motion rotary magnetic exciters, rotary exciters,stepping motors and electrical to mechanical energy transducers. Insimilar fashion, the electrical windings which magnetically energize thetorsionally resilient coupling member are variously called coils,windings, electrical windings, and turns.

ELECTRICAL DESCRIPTION In FIG. 10A of the drawings there is shown anelectrical circuit which-may be employed to energize the incrementalmotion rotary magnetic exciter located at one .end of the torsion shaftmember 30 shown in F IG.. 3 of the drawings. In the FIG. 10A circuitry,the electrical winding 411 corresponds to one of the exciter coils 60and 61 of the FIG. 3 drawing.

The circuitry of FIG. 10A includes electrical winding 41], connectedwith two electrical inductance coils 399 and 431, and. two electricalswitching elements such as transistors 407 and 439, a source ofelectrical energy 427 which is connected via terminals 395, 425 andground terminals 409 and 4l0 to the transistors 407 and 439 and toelectrical resistance elements 397- and429. The transistor devices 407and 439 in FIG. 10A are controlled as to their ON or OFF state bysignals applied to the base electrodes via terminals 473 and 441.

FIG. 10B of the drawings shows an electrical waveform such as may beencountered during transient operation of transistor 407 or 439 in FIG.10A; the waveform of FIG. 10B consisting of a period of rising voltage443, a period of stable voltage 447 and a period of falling voltage 449together with time indications as to the duration of significantportions of the waveform l..i5 V V V.

FIG. C of the drawings, which was described earlier in thisspecification, represents a magnetic hystere-; sis curve such as mayexist for the ferromagnetic structure associated with the incrementalmotion rotary magnetic exciter electrical winding 411 in FlG 1 0 Themanner in which the circuitry of FIG. 10A causes the ferromagneticstructure associated with winding 411 to be excited and to undergo arapid decrease in magnetic flux coupling once de-energized may bedescribed in terms of the electrical energy relationships that are wellknown for an electrical inductance coil. This description isconveniently commenced by assuming that the circuit of FIG. 10A wasexcited at some previous time and has been allowed to remain in thesteady state excited condition until all currents and voltages appearingtherein are stabilized. In this steady state, stabilized condition withtransistor Q1, 407 in the conducting state, and transistors O2, 439, inthe nonconducting state, a current labelled I, and flowing as indicatedby arrow 421 will pass through resistor 429, inductance coil 431,winding 411, and transistor 407. Typically for one embodiment of theinvention, the current I; may be in the order of five amperes wherevoltage 427 is in the order of plus 48 volts, the inductance of winding411 is near 3 millihenrys, the inductance of coils 399 and 431 is nearmillihenrys and the resistance of resistors 397 and 429 is avaluebetween 0 and 8 ohms. Resistors 397 and 429 are given such value as willlimit the steady state current in the inductance coils 399 and 431 to apredetermined am-' P dZ'. .L With the steady state current i, flowing inthe FIG. 10A circuit, the voltage developed across inductance coil 431has the polarity shown by the plus and minus signs 433 and 435respectively with the top end terminal of inductance 431 being positivewith respect to the bottom end terminal. In the case of coil 411, theright.

hand end terminal is positive with respect to the left hand end terminalas shown by the plus sign 415 and the minus sign 413. During the steadystate interval, a current is also established in inductance coil 399 andresistor 397, this current is labelled I and is indicated by the arrow423 in FIG. 10A. Both the current I and the current l flow into circuitnode 405 and thence into the switching element represented by transistor407 and thence to the ground terminal 409; in other words, a totalsteady state current often amperes flows in the electrical switchingelement 407 for the FIG. 10 embodiment of the invention. The steadystate current condition for the circuit of FIG. 10A represents thatcondition which exists when the rotor associated with winding 411 isbeing held in magnetic engagement with the associated stator, thissteady state condition being also similar to the condition existing whena rotor is being re-attractecl to a position of stator engagementfollowing a release and movement of the rotor. The events following asteady state rotor holding consist of turning OFF the switching elementwhich has been ON, i.e. transistor O1, 407 and turning ON the oppositeswitching element; i.e. transistor O2, 439; wherein, in the FIG. 10Acircuitry, this produces the effects de- -SQIi QdFK Q QW t v e ulybsrt tlqs a triqa .sni shinsjs emsm traasistor Q2,

'439 is turned ON, the steady state current I, 421 is diverted from thepath flowing through winding 411 into a path passing through electricalswitching element 439. The removal of current I; from winding 411proiduces an instantaneous change of voltage polarity across winding 411as the energy which has been stored in the inductance of winding 411,attempts to maintain the current I, flowing in the windings.

Maintenance of current If is in accordance with the well knownproperties of an electrical inductance coil, that of maintaining apreviously established current .the waveform shown in FIG. 10B, theinstantaneous polarity of the voltage across winding 411 now being thatindicated by the symbols 417 and 419.

Interruptions of the path by which current II, 423, has been flowingthrough-electrical switching element transistor 407 produces aninstantaneous change of voltage polarity across inductance coil 399, thenew polarities for inductance coil 399 being indicated by symbols 404and 402, this change of polarity being also according to the previouslymentioned behavior of an electrical inductance coil having aninterruption of a steady state current flow. Since both the electricalenergy stored within winding 411 and that stored in inductance coil 399,tend to place circuit node 405 at some positive potential uponinterruption of the steady state current path through switching elementtransistor 407, there are, in reality two sources of energy causing thepreviously mentioned rise shown by region 443 of the FIG. 10B curve. Inthe absence of a voltage limiting mechanism, acting on node 40S, thevoltage at node 405 will increase to some high value even as high asseveral thousand volts as a result of the energy stored in winding 411and inductance coil 9. 1....w t

Transistor Q1, 407 in addition to serving as a switching device, alsoacts as a voltage limiting mechanism FIG. 10A have a secondary breakdowncharacteristic tending to limit the voltage at circuit node 405 to about160yvolts, when a current of 10 amperes is flowing.

Since both the winding 411 and the inductance coil 399 obey thefundamental relationship of V=Ldi/dt, where V is the voltage developedacross an inductance L that is incurring a current change at the rate ofdi/dt, both the rate at which current can change in winding 411, and therate at which energy can be withdrawn from the inductance of winding 411and therefore the rate at which magnetic flux between motor rotor andstator can be removed, are dependent upon the magnitude of the voltageallowed at circuit node 405. If a transistor device having a highervoltage secondary breakdown characteristic than the 2N3773 is employedat the O1, 407 position, the energyremoval process will occur morequickly than in the microsecond interval indicated at 451 in FIG. 10B.Power transistor devices of the NPN type are available with a reversevoltage rating higher than 160 volts, however, these transistors may notbe appropriate for the present invention since the voltage developed atnode 405 will readily exceed any reverse voltage breakdown capabilityfound in a power transistor not designed for operation as an energydissipating device in the secondary breakdown mode of operation. The 2N3773 has a secondary breakdown energy dissipatingcharacteristic which isrelatively high in voltage rating considering the present state of thetransistor art. The energy dissipation which occurs in transistor Q1,407, represents a change in magnetic flux within the ferromagneticstructure associated with electrical winding 411 from they point 461 tothe point 463 on the magnetic hysteresis, B-H curve of FIG. C.

Although the transistors employed as electrical switching elements 407and 439 limit the voltage appearing at circuit node-405 to a value near160 volts, it is significant to realize that this 160 volt limitationmay in fact permit more rapid discharge of the energy stored in winding411 than would a mechanical switch device wherein energy stored in thewinding inductance would be dissipated in the form'of an electrical arc.The voltage developed across an established electrical arc wherein thereare ionized molecules of vmetal and high temperature gases provides acurrent flow path that may have lower electrical impedance than that ofthe 2N3.773 transistors operating in 160 volt secondary breakdowndissipation mode.

During the 150 microsecond portion 477 of the curve shown in FIG. 10B,energy is being extracted from both electrical winding 411 andinductance coil 399 and is being dissipated in the secondary breakdownaction of transistor 01,407; the duration of this enregy dissipatingperiod, that is the length of the curve position 447 in FIG. 103 beingdependent upon the amount of energy stored in winding 411. For instance,where the voltage across transistor O1, 407 is the previously mentionedI60 volts and the inductance of winding 411 is 3 millihenrys, and theinitial winding current is 5 amperes, the instantaneous rate of changeof current, a'i/dt, is near fifty three times 10 amperes per second andthe energy stored within winding 411 should be discharged in about I00microseconds of time. Following discharge of the energy stored withinwinding 41 l, the Current in transistor O1, 407, decreases from the tenampere value which prevailed while both inductance coil 399 and winding41! were feeding current into node 405 to some current value near fiveamperes; the decrease in current flow in transistor Ql 407, resulting ina decreased voltage across the transistor 01, as is shown by the portion449 of the curve in FIG. 108.

One of the important features of the FIG. 10A circuit is that byselecting inductance coil 399 to have an inductance much larger thanthat of the winding 411,

there is sufficient energy stored within the inductance coil 399following complete discharge of winding 411 to permit energy frominductance coil 399 to immediately and automatically establish a reversecurrent in winding 411. This reverse current is effective to overcomethe residual magnetism component of flux in the ferromagnetic structureassociated with winding 411 and to move the operating point of theferromagnetic structure in the motor from point 463 in FIG. 10C to point467. The desirability of this reverse current en- I ergy-storage is oneof the major purposes for including It is to be noted that resistanceelement 397 removes energy from inductance coil 399 during both theperiod when transistor O1, 407 is removing energy and also during theperiod when inductance coil 399 is providing reverse current in winding41 1; however, so that the combination of energy removal by resistance397 and transistor 407 do not prematurely exhaust the energy availablefrom inductance coil 399, it is necessary that consideration be given tothe relative quantities of energy stored and the energy dissipatingrates of the circuit components. In the FIG. 10A embodiment of thecircuit where a 48 volt powersourceis used, it has been foundsatisfactory to provide an inductance of about thirty millihenrys or tentimes the inductance of winding 411 for the inductance coils 399 and431.

t Several features make the circuit in FIG. 10A partic- .path in acircuit node, such as nodes 437 and 405 in FIG. 10A, into the windingsof the torsionalstepping motor, pre-established current steering beingin lieu of the usual motor energizing technique of closing an electricalcircuit and waiting for the' current to attain a desired value. In aloadwhich includes an inductive device, such as winding 411, the use ofpre-established currents thatare regulated by a larger inductanceelement is a speed increasing factor. 2. The circuit of FIG. 10A employsthe energy storing capability of an auxilia ary electrical inductancecoil, i.e. coil 399, to collect over a long period of time the energyneeded during transient energization events for the load winding 411;the energy release characteristics of the storage inductance coil 399being almost ideally suited for the excitation needs of an inductiveload member such as winding 411. 3. The circuit insofar as load windings41 1 are concerned acts as a constant current generator, that is, itprovides current having a magnitude substantially independent of thevoltage appearing across load winding 411. As a result of the energystoring capability of the inductance coils 399 and 431, the total powersupply energy which must be dissipated to achieve the constant currentcharacteristic is much less than would be the case if conventionalconstant current circuits employing large voltages and high seriesresistances or dynamic constant current generators were employed toexcite winding 411. 4. The circuit of FIG. 10A ideally meets the fastflux reversal demands of winding 411 by providing both a high voltageenergy dissipating 'meenergy stored in winding 411, the tire-establishedvoltage across transistor O1, 407 generates in winding 41 1 a reversecurrent for overcoming residual magnetism in the ferromagnetic structureof the stepping motor; this reverse current representing a diversion ofsome energy from inductance coil 399 from the dissipation mecha-

1. In an improved incremental motion apparatus combination thatincludes: first electrical to mechanical energy transducer meansincluding a first rotor means for converting electrical energy intoincremental rotation mechanical energy; second electrical to mechanicalenergy transducer means, including a second rotor means, for convertingelectrical energy into incremental rotation mechanical energy; a sourceof electrical energy; and electrical exciting means coupled to saidsource of electrical energy for exciting said first and second energytransducer means; the improvement which comprises: rotationallyresilient coupling means joined at one end thereof to said first rotormeans and at the other end thereof to said second rotor means, fortorsionally storing and for transmitting between said first and secondrotor means, portions of said incremental rotation mechanical energy;current determining means within said electrical exciting means forestablishing from said source of electrical energy a limited flow ofelectrical current; and current steering means for steering said limitedflow of electrical current alternately into said electrical-tomechanicalenergy transducer means or around said electricalto-mechanical energytransducer means in diversion thereof.
 2. An incremental motionapparatus combination as in claim 1 wherein said current steering meansincludes two electrical switching elements connected with electricalwindings in each transducer means and connected to steer either of twolimited currents into said transducer means electrical windings inopposite direction therein, whereby current flowing in either possibledirection is realized in said electrical windings in each transducermeans.
 3. An incremental motion apparatus combination as in claim 1wherein said current determining means includes in the current flow paththereof one or more current magnitude controlling elements capable ofestablishing, at least temporarily in a transducer means electricalwinding, a current that is substantially defined by the currentmagnitude controlling element and substantially independent of inducedvoltages in the transducer means windings; whereby current in thetransducer means windings can increase from zero to a desired amplitudeand direction in a time shorter than the L/R time constant of thetransducer means electrical windings, said shorter time also beingpotentially shorter than the mechanical oscillation period of thecombined resilient coupling means and rotor means in said transducermeans, following current steering changes in winding excitation.
 4. Anincremental motion apparatus combination as in claim 3 wherein saidcurrent magnitude controlling elements include an electrical inductancecoil; whereby current in the transducer means windings rapidly attains adesired amplitude and direction following current steering acts byvirtue of magnetic field energy storage within said electricalinductance coil notwithstanding voltages inductively induced in saidtransducer means electrical windings immediately following currentsteering acts.
 5. An incremental motion apparatus combination as inclaim 4 wherein said electrical inductance coil has an electricalinductance at least five times the inductance of said transducer meanselectrical windings.
 6. An incremental motion apparatus combination asin claim 4 wherein said electrical inductance coil has an electricalinductance near the range of 5 to 10 times the inductance of saidtransducer means electrical windings.
 7. An incremental motion apparatuscombination as in claim 2 wherein said electrical switching elements aresolid state electronic switching devices.
 8. An incremental motionapparatus combination as in claim 7 wherein said solid state electronicdevices are bipolar power transistors.
 9. An incremental motionapparatus combination as in claim 8 wherein said bipolar powertransistors are transistors capable of repeatedly dissipating electricalenergy in the secondary breakdown mode of operation.
 10. An incrementalmotion apparatus combination as in claim 3 wherein said currentmagnitude controlling elements include an electrical inductance coil andsaid electrical switching elements connected to steer continuouslyflowing current are transistors.
 11. An incremental motion apparatuscombination as in claim 1 wherein said current steering means includestwo bipolar transistor electrical switching elements and said currentdetermining means includes two electrical inductance coils; with saidsource of electrical energy, said transducer means electrical windings,said two bipolar transistors and said two electrical inductance coilsbeing connected into a bridge circuit wherein said two electricalinductance coils form upper bridge arms, and said two bipolartransistors form lower bridge arms with said transducer means electricalwindings being connected across the bridge between the two junctions ofa bipolar transistor and an electrical inductance coil and with thesource of electrical energy being connected between the top and bottompoints of the bridge between the junction of two inductance coils andthe junction of two transistors.
 12. An incremental motion apparatuscombination as in claim 8 wherein said bipolar transistors are capableof operating at voltages at least three times the nominal operatingvoltage of said source of electrical energy during an interval whenenergy stored in the magnetic field of said transducer means electricalwindings is being removed therefrom; whereby said magnetic field energyis removed quickly by energy transfer from the electrical windings at arelatively large voltage level and said transistors are capable ofrepeated acts of dissipation without injury.
 13. An incremental motionapparatus combination as in claim 3 wherein said current magnitudecontrolling element is an energy dissipating non-energy storing elementand said source of electrical energy has a voltage potential larger thanthe resistance voltage drop in the transducer means electrical windingswhile a predetermined winding current flows therein.
 14. An incrementalmotion apparatus combination as in claim 13 wherein said energydissipating non-energy storing element is an electrical resistanceelement.
 15. An incremental motion apparatus combination as in claim 13wherein said energy dissipating non-energy storing element is a multipleport active electronic device.
 16. An incremental motion apparatuscombination as in claim 1 wherein said current steering means includesopen loop, non-rotor rotation responsive logical circuitry means forgenerating electrical switching means timing signals; wherebyincremental movement of said rotor means in saidelectrical-to-mechanical energy transducer means is governed by burstsof electrical energy supplied in accordance with timing circuitry insaid logical circuitry means and without regard for past movements ofsaid rotor means.
 17. An incremental motion apparatus combination as inclaim 1 wherein both of said electrical-to-mechanical energy transducermeans include electrical windings, said source of electrical energy is adirect current source, said electrical exciting means including saidcurrent determining means generating from said source of direct currentenergy two continuously flowing currents having magnitudes when flowingin said electrical windings that are largely independent of voltagesdeveloped therein, and wherein said current steering means includesfirst current steering means for steering one of said continuouslyflowing currents both into one of said electrical windings and also awayfrom said one electrical winding, second current steering means forsteering the other of said continuously flowing currents both into theother of said electrical windings and also away from said otherelectrical winding, and third current steering means cooperative withsaid first and second current steering means for steering either one ofsaid continuously flowing electrical currents through both of saidelectrical windings.
 18. An incremental motion apparatus combination asin claim 17 wherein said current determining means are energy storingelectrical inductance coils.
 19. An incremental motion apparatuscombination as in claim 18 wherein said first, second, and third currentsteering means each include transistor devices.
 20. An incrementalmotion apparatus combination as in claim 19 wherein said source ofdirect current electrical energy, said electrical windings, and saidtransistor devices are connected into an electrical bridge circuitwherein the upper arms of said bridge circuit each include one of saidelectrical inductance coils, the lower arms of said bridge circuit eachinclude a transistor device, said source of direct current energy isconnected across the top and bottom points of said bridge circuitbetween the junction of said inductance inclusive arms and the junctionof said transistor inclusive arms, said electrical windings beingconnected in series, with the non-joined end terminals thereof beingconnected across the horizontal points of said bridge circuit betweenthe two junctions of an electrical inductance inclusive arm and atransistor inclusive arm, and a third transistor device is connectedbetween the joined ends of said electrical windings and the lower pointof said bridge circuit, being therefore connected between the joinedends of said windings and the junction of said two transistor inclusivearms.
 21. In a method for actuating an intermittent motion apparatus, ofthe type including two electrical-to-mechanical transducer devices eachhaving a stator portion with associated electromagnetic windings and anincrementally Rotating rotor portion that is joined to the oppositerotor portion by a torsionally resilient coupling member, and includingthe steps of: electrically rotating the rotor portion of a first one ofthe transducer devices into a first rotor incremental position byelectrically exciting the electromagnetic windings of the firsttransducer device; electrically moving the rotor portion of the secondtransducer device against torsional force from the resilient couplingmember into a nearby second rotor incremental position by electricallyexciting the electromagnetic windings of the second transducer device,the torsionally resilient coupling member being thereby distortedthrough part of a rotor increment in a first rotational direction;electrically releasing the rotor portion of the first transducer devicefrom the first rotor incremental position under the urging of torsionalforce from the distorted resilient coupling member, thereby allowing thetorsional force to accelerate the first rotor portion away from thefirst rotor incremental position toward a position of zero distortion inthe resilient coupling member and a new first rotor incremental positionwherein distortion of the resilient coupling member will be part of arotor increment and reverse that of said first rotational direction;electrically attracting the rotor portion of the first transducer deviceto the new first rotor incremental position by re-exciting the firsttransducer device; and electrically freeing the rotor portion of thesecond transducer device from the second rotor incremental positionunder the urging of torsional force from the distorted resilientcoupling member, thereby allowing the torsional force to accelerate thesecond rotor portion away from said second rotor incremental positiontoward a position of zero distortion in the resilient coupling memberand a new second rotor incremental position wherein distortion of theresilient coupling member is in the first rotational direction;electrically drawing the rotor portion of the second transducer deviceto the new second rotor incremental position by re-exciting the secondtransducer device; an improved method for electrically releasing andelectrically freeing said rotor portions while avoiding during saidsteps substantial dissipation of the potential energy stored within saidresilient coupling member, said improved method comprising the steps of:establishing within a first electrical energy dissipating element afirst energy dissipation rate during said electrically releasing step;transferring energy stored within the inductance of said electromagneticwindings of said first transducer device into said first electricalenergy dissipating element by adding to the energy of said first energydissipation rate, in said first electrical energy dissipating element,during said electrically releasing step, the magnetic flux stored energyof said electromagnetic windings of said first transducer device;diverting a part of the first energy dissipating rate energy from saidfirst electrical energy dissipating element into said electro-magneticwindings of said first transducer device following completion of saidtransferring energy step, continuing the diverting act until residualmagnetism flux in said first rotor and stator portions is overcome;whereby said transferring and diverting steps may be accomplished with asingle continuous and noninterrupted connecting of said electromagneticwindings of said first transducer device with said first electricalenergy dissipating element; setting up within a second electrical energydissipating element a second energy dissipating rate during saidelectrically freeing step; conducting energy stored within theinductance of said electromagnetic windings of said second transducerdevice into said second electrical energy dissipating element by addingto the energy of said second energy dissipating rate, in said secondelectrical energy dissipaTing element, during said electrically freeingstep, the magnetic flux stored energy of said electromagnetic windingsof said second transducer device; and steering a part of the secondenergy dissipating rate energy from said second electrical energydissipating element into said electromagnetic windings of said secondtransducer device following completion of said conducting energy step,continuing the steering act until residual magnetism flux in said secondrotor and stator portions is overcome; whereby said conducting andsteering steps may be accomplished with a single continuous andnon-interrupted connecting of said electromagnetic windings of saidfirst transducer device with said second electrical energy dissipatingelement; whereby both the stored energy component of the magnetic fluxlinking said rotor and stator portions and the residual magnetismcomponent of said linking flux are removed from said transducer devicesquickly and before said torsionally resilient coupling member hassignificantly expended stored potential energy in moving said rotorportions in the presence of decaying magnetic flux.
 22. An improvedmethod for electrically releasing and electrically freeing as in claim21 wherein said acts of establishing a first energy dissipation rate ina first electrical energy dissipating element and setting up a secondenergy dissipation rate in a second electrical energy dissipatingelement include developing across said elements a voltage that is largerthan the supply voltage employed to excite said transducer devices. 23.An improved method for electrically releasing and electrically freeingas in claim 22 wherein said acts of establishing a first energydissipation rate in a first electrical energy dissipating element andsetting up a second energy dissipation rate in a second electricalenergy dissipating element include transferring the energy stored inexternal inductance coils into said first and second electrical energydissipating elements.
 24. An improved method for electrically releasingand electrically freeing as in claim 21 wherein both of said steps ofestablishing and setting up are respectively preceded by the step ofremoving from said transducer device electromagnetic windings a flow ofexternally derived transducer exciting current.
 25. An improved methodfor electrically releasing and electrically freeing as in claim 21wherein the method also includes the additional step of: maintainingsaid electromagnetic windings in a non-energized state during a timeinterval commencing with the termination of said steering and divertingacts following the overcoming of said residual magnetism flux andcontinuing until said rotor portion has moved substantially toward asucceeding incremental position.